1. Field of the Invention
This invention relates to a sound control unit and a sound system.
2. Description of Related Art
FIG. 5 is a schematic diagram showing an example in which a bus is mounted with a conventional sound system. In FIG. 5, reference numeral 101 denotes a body of the bus, reference numeral 102 a ceiling of the bus, reference numeral 103 right and left racks disposed under the ceiling 102, reference numeral 104 right and left speaker systems disposed on the respective racks 103, reference numeral 105 speaker units and reference numeral 106 a sound reproducing unit for inputting a sound signal to the speaker units 105.
FIGS. 6A and 6B are schematic drawings showing a double driving type speaker system and a single driving type speaker system, respectively, of the speaker system 104. FIG. 6A shows a double driving type speaker system 104A having two spaces therein.
Referring to FIG. 6A, reference numeral 105A denotes two front-radiating speaker units, reference numeral 105B an auxiliary speaker unit, reference numeral 120A a closed inner space required for disposing therein and driving the front-radiation speaker units 105A, and reference numeral 120B a closed inner space or an inner space having an open plane required for disposing therein and driving the auxiliary speaker unit 105B.
FIG. 6B shows a single driving type speaker system 104B having a single space volume therein. Referring to FIG. 6B, reference numeral 105C denotes two front-radiation speaker units, and reference numeral 120C a closed inner space required for disposing therein and driving the front-radiation speaker units 105C.
Each of the speaker units 105A, 105B, and 105C is provided with a driving voice coil and a magnetic circuit for driving a diaphragm in response to the inputted sound signal.
FIG. 7 is an internal block diagram showing the configuration of the sound reproducing unit 106 in FIG. 6. Referring to FIG. 7, reference numeral 107 denotes a selector for selecting a sound source signal outputted from a sound source, reference numeral 108 an amplifier for amplifying the selected sound source signal and outputting the sound signal, and reference numeral 109 a plurality of driving voice coils provided for the respective speaker units for inputting the sound source signal outputted from the amplifier 108.
The operation of the conventional sound reproducing unit will be described.
Although the speaker system inside the bus is, as shown in FIG. 5, a stereo type arranged on the right and left sides, the operation of one speaker system will be described for the sake of simplicity. Various kinds of sound source signals (TUNER, TAPE, CD, AUX) from a tuner, a cassette tape player, a compact disc (CD) player, and other sound source devices are inputted to the selector 107 in FIG. 7. The selector 107 selects one sound source out of various kinds of sound sources in accordance with the selecting operation and inputs it to the amplifier 108. The amplifier 108 amplifies this sound source signal to output it as a sound signal (AS), and inputs it to the driving voice coil 109 of each of the speaker units.
In case of the double driving type speaker system 104A, the sound signal inputted to the driving voice coils 109 of the two front-radiating speaker units 105A vibrates the diaphragm coupled to a bobbin to which the driving voice coil 109 is fixed, thereby radiating a sound to the front. Further, the sound signal inputted to the driving voice coil 109 of the auxiliary speaker unit 105B radiates the sound to the rear of the front-radiating speaker units 105A so as to complement the vibrations of the front-radiating speaker units 105A. As a result, in the double driving type speaker system 104A, the front-radiating speaker units 105A inside the closed inner space 120A radiate bass enhanced by the aide of the radiation from the auxiliary speaker unit 105B inside the closed inner space 120B.
On the other hand, in case of the single driving type speaker system 104B, the sound signal inputted to the driving voice coils 109 of the two front-radiating speaker units 105C vibrates the diaphragm coupled to the bobbin to which the driving voice coil 109 is fixed, thereby radiating a sound to the front. That is, in the single driving type speaker system 104B, the sound is radiated only by the front-radiating speaker units 105C inside the closed inner space 120C having a closed inner space or an opening plane.
In any driving type speaker systems, the closed inner space virtually determines the minimum resonance frequency and the steepness of the resonance characteristics which define the limit of bass reproduction, and those members of different kind of diaphragm and the supporting system which constitute the speaker unit, as well as by the member constants determines the treble characteristics.
FIG. 8 is a graph showing examples of the sound characteristics of the speaker system in the sound system for a bus. In FIG. 8, the characteristic curve F1 on the upper side represents an output sound pressure frequency characteristic, and the characteristic curve Z1 on the lower side represents an impedance characteristic having the output sound pressure frequency characteristic. In FIG. 8, the frequency f0 is the limit of the minimum resonance frequency at which the bass is reproducible, and the steepness of the resonance frequency is generally called as a Q factor.
The conventional sound system thus arranged as described above, in case of the double driving type speaker system, needs the auxiliary speaker for enhancing the bass in addition to the two front-radiating speaker units. Further, the speaker cabinet has the closed inner space for the auxiliary speaker unit in addition to that for the front radiating speaker units, which complicates the structure of the speaker cabinet, bringing about an increase in the cost of the sound system.
In addition, the auxiliary speaker unit succeeds in synchronization (following-up) in the same phase in the vibration-sound radiating region relating to the bass reproduction of the front-radiating speaker units. In the vibration-sound radiating region relating to the treble reproduction, however, the auxiliary speaker unit fails in synchronization in the same phase with the increase in the number of vibrations. In this kind of frequency region in which synchronization cannot accomplish, once it comes to the worst vibrating conditions, the vibration amplitude of the auxiliary speaker unit becomes antiphase to the vibration amplitude of the front-radiating speaker units, resulting in the occurrence of distortion in sound. Further, a gain in the weight of the speaker system causes an increase in the cost of the bus itself and the specific fuel consumption of the bus resulting from the fortification, or the like, as a measure to be taken for safety.
On the other hand, in case of the single driving type speaker system, it is necessary to widen the closed inner space in order to attain good bass reproduction characteristics. As a result, the speaker cabinet becomes large in size and weight, a rate of the occupied volume inside the bus becomes large, and the cost of the bus itself and the specific fuel consumption of the bus increase due to the fortification, or the like, as a measure to be taken for safety. Even in case the speaker unit is a so-called bass-reflex (bass reflection) type having a partial opening so as to make the inner space smaller to a certain degree, the structure of the speaker cabinet becomes complicated and therefore a measure must be taken to secure dust proofing, leading to an increase in the cost of the sound system.